Platinum/triene complexes useful for hydrosilylation catalysis

ABSTRACT

Novel platinum/olefin complexes, useful for the hydrosilylation curing catalysis of hardenable organopolysiloxane compositions, are facilely prepared by reacting a platinum halide with at least one alkali or alkaline earth metal carbonate or bicarbonate in the presence of an aliphatic triene ligand having the general formula: ##STR1## wherein R 1  is a linear or branched chain alkyl radical having from 1 to 6 carbon atoms, and R 2  is R 1  or a linear or branched chain alkenyl radical having from 2 to 16 carbon atoms and at least one site of ethylenic unsaturation, and said complex having a ratio, in gram-atoms of halogen to gram-atoms of platinum, ranging from virtually 0 to 4.

CROSS-REFERENCE TO RELATED APPLICATION

My copending application, Ser. No. 811,393, filed concurrently herewithand assigned to the assignee hereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to novel platinum/olefin complexes, and,more especially, to platinum/triene complexes useful as hydrosilylationcatalysts, to the preparation thereof and to organopolysiloxanecompositions comprising such catalytic complexes.

2. Description of the Prior Art

Many compounds and complexes of platinum have to date been proposed tothis art to promote the addition reaction of an organohydropolysiloxanehaving .tbd.SiH groups to a diorganopolysiloxane containing hydrocarbonradicals which are alkylenically unsaturated, for the purpose of formingan addition product comprising an added silicon-carbon bond.

This addition reaction can be represented schematically in the followingmanner: ##STR2##

One of the first such catalysts was chloroplatinic acid, as described inU.S. Pat. No. 2,823,218, or platinum metal arranged on a finely dividedsupport, as described in U.S. Pat. No. 2,970,150.

In U.S. Pat. Nos. 3,159,601 and 3,159,602, platinum/olefin complexeswere proposed for the purpose of reducing the disadvantages inherent inthe use of finely divided platinum or chloroplatinic acid, thedisadvantages being related to poisoning of the catalyst and to itsexcessively low reactivity. With the same object, in U.S. Pat. No.3,220,972, the reaction products of platinum derivatives with alcohols,aldehydes and ethers were proposed as a catalyst.

More recently, in U.S. Pat. Nos. 3,715,334, 3,775,432 and 3,814,730,there were proposed complexes of platinum and vinylsiloxane, treatedwith a base, in which complexes the ratio of halogen to platinum isbetween 0, or a decimal number close to 0, and approximately 1.

In European Pat. No. 57,459, platinum/styrene complexes treated with abase are described, in which the ratio of halogen to platinum(calculated in gram-atoms of platinum and halogen) is greater than 1 butless than 4.

The platinum complexes described above have admittedly enabled advancesin the state of the art, but they have at least one of the followingdisadvantages:

(1) they are unstable and display low catalytic activity after arelatively short storage time, on the order of one month or less;

(2) they display insufficient reactivity at a low concentration;

(3) they are particularly difficult to prepare in a simple andreproducible manner, especially as regards those described in said '459European patent.

SUMMARY OF THE INVENTION

Accordingly, a major object of the present invention is the provision ofnovel platinum complexes which are conspicuously devoid of the aforesaiddisadvantages and drawbacks, or which, at very least, display same tosuch a limited extent that the commercial attractiveness thereof is notimpaired.

Briefly, the present invention features preparing a platinum/olefincomplex hydrosilylation catalyst, by reacting a platinum halide with atleast one basic compound comprising the alkali metal carbonates orbicarbonates, or the alkaline earth metal carbonates or bicarbonates, inthe presence of an olefin ligand which is an aliphatic trienehydrocarbon having the general formula: ##STR3## in which R₁ is a linearor branched chain alkyl radical having from 1 to 6 carbon atoms, R₁preferably being a methyl radical, and R₂ is also an alkyl radicalhaving from 1 to 6 carbon atoms, or a linear or branched chain alkenylradical having from 2 to 16 carbon atoms and at least one site ofethylenic unsaturation, to obtain a platinum/triene complex possessing aCl/Pt ratio, in gram-atoms of halogen to gram-atoms of platinum, rangingfrom virtually 0 to 4, inclusive.

DETAILED DESCRIPTION OF THE INVENTION

More particularly according to the present invention, representativetrienes having the aforesaid formula (I) include:

(i) β-myrcene having the formula: ##STR4##

Processes for the preparation thereof are noted at reference 6180, TheMerck Index (10th Edition).

(ii) β-farnesene having the formula: ##STR5##

Processes for the preparation thereof are noted at reference 3874, TheMerck Index (10th Edition).

(iii) β-springene having the formula: ##STR6## described by B.V. Burgeret al., Tetrahedron Lett., 6221 (1978).

For carrying out the process of the invention, it is desirable to use alarge molar excess of ligand relative to the platinum halide; aligand/platinum halide molar ratio ranging from 10 to 30 is preferablyused.

The amount of halogen chemically combined in the platinum/trienecomplexes of the invention can be determined by any known suitablemethod, in particular by the disodiumbiphenyl technique described inAnalytical Chemistry, 22, 311 (February 1950).

The same applies to evaluating the platinum content of the complexesaccording to the invention. A suitable method is that employing atomicspectroscopy, as described by R. Dockyer and G.E. Haives, The Analyst,84, page 385, (1959).

To carry out the process according to the invention, chloroplatinic acidof the formula:

    H.sub.2 PtCl.sub.6.nH.sub.2 O

can be used, the same being readily commercially available in itshexahydrate form (n=6).

Metal salts of chloroplatinic acid, such as, for example, NaHPtCl₆.nH₂O, KHPtCl₆.nH₂ O, Na₂ PtCl₆.nH₂ O and K₂ PtCl₆.nH₂ O, can also be used.

PtCl₄.nH₂ O and the halides of platinous type, such as PtCl₂, Na₂PtCl₄.nH₂ O, H₂ PtCl₄.nH₂ O, NaHPtCl₄.nH₂ O, KHPtCl₄.nH₂ O and K₂ PtBr₄,can also be used.

Chloroplatinic acid in its hydrated or anhydrous form constitutes thepreferred starting material according to the invention.

The process of the invention is, furthermore, preferably carried out inan organic solvent in order to dissolve the platinum halide and thecomplex formed. This solvent is preferably selected from among a linearor branched chain aliphatic alcohol having from 1 to 6 carbon atoms,preferably isopropanol, an aromatic organic solvent or a saturatedhydrocarbon such as benzene, toluene, xylene and hexane.

As the basic compound, alkali metal carbonates and bicarbonates andalkaline earth metal carbonates and bicarbonates are used, such assodium carbonate, sodium bicarbonate, potassium carbonate and potassiumbicarbonate, preferably in an excess such that the Cl/Pt ratio fallswell within the aforenoted range.

The preferred basic compounds are alkali metal bicarbonates, whichenable the chemical reduction of the catalyst to its metallic form to beavoided with certainty.

The reaction temperature generally ranges from 20 to 120° C., preferablyfrom 60 to 100° C., for a period typically ranging from 5 min to 2hours.

The final Cl/Pt ratio in the product complex depends upon the choice ofthe starting halide, the amount of basic compound added and the reactiontemperature.

The reaction time essentially depends on the temperature, this timebeing shorter the higher the temperature.

The complexes for which the Cl/Pt ratio ranges from virtually 0 to 2,inclusive, are preferred, since they are more soluble in the solventused in their preparation, and they show greater reactivity in theorganopolysiloxane compositions.

By a Cl/Pt ratio "virtually equal to 0", there is intended a ratio whichcan be equal to 0.1 or less without being zero. It has in fact beenobserved that it is almost impossible to have a ratio precisely equal to0, since traces of inorganic chlorine which originate from the reactionby-products, and which are extremely difficult to remove completely,always persist in the reaction medium.

The platinum complex according to the invention can be used to catalyzeorganopolysiloxane compositions which entail hydrosilylation reactionsin their hardening or curing. Before use, this complex is preferablydiluted in an organic solvent compatible with silicones (toluene,hexanol, chlorobenzene or isopropanol, for example) or in a vinylatedsilicone oil.

Such compositions can be compositions which harden to elastomers at roomtemperature (RTV), of the type described in U.S. Pat. Nos. 3,220,972 and3,814,730, which can be used, inter alia, for impregnation, coating,encapsulation, molding and dental impressions.

These compositions can be coating compositions, either with or withoutsolvent, which can be used to make a material non-sticking, asdescribed, for example, in U.S. Pat. Nos. 4,057,596, 4,071,644 and4,162,356 and British Pat. No. 1,374,732 for the solvent-freecompositions, and in U.S. Pat. Nos. 3,527,659, 4,028,298 and BritishPat. No. 1,240,520 for the compositions with solvents.

These compositions are generally stored before use as two components ortwo packs, one of the components containing the catalyst and generallyat least a portion of the organopolysiloxane possessing organic radicalswhich are alkylenically unsaturated. The other component contains, inparticular, the organohydropolysiloxane, and the two components aremixed, as required, immediately before use.

The alkylenically unsaturated organopolysiloxane and theorganohydropolysiloxane can be cyclic or substantially linear;advantageously, they can be a polymer or copolymer.

The present invention, hence, also relates to an organopolysiloxanecomposition containing:

(1) at least one organopolysiloxane which possesses, per molecule, atleast two alkylenically unsaturated groups bonded to a silicon atom;

(2) at least one organohydropolysiloxane which possesses, per molecule,at least three .tbd.SiH groups; and

(3) a catalytically effective amount of a platinum/triene complexaccording to the present invention.

The compound (1) is advantageously an organopolysiloxane comprisingsilyloxy units of the formula: ##EQU1## in which Y is an alkylenicallyunsaturated hydrocarbon group having from 2 to 4 carbon atoms,inclusive. Y can be, for example, a vinyl, propenyl, allyl or butenylgroup, with the vinyl group being the preferred.

Z is a monovalent hydrocarbon group which does not adversely affect theactivity of the catalyst. Z is generally selected from among alkylgroups having from 1 to 8 carbon atoms, inclusive, such as methyl,ethyl, propyl and 3,3,3-trifluoropropropyl groups, and aryl groups suchas xylyl, tolyl and phenyl, a ranges from 1 to 3, b ranges from 0 to 2and a+b ranges from 1 to 3, all other units optionally being units ofthe formula: ##EQU2## in which Z is defined as above and c has a valueranging from 0 to 3.

The compound (2) is advantageously an organohydropolysiloxane containingsilyloxy units of the formula: ##EQU3## in which W is a monovalenthydrocarbon group which does not adversely affect the activity of thecatalyst and which conforms to the same definition as Z; d has a valueranging from 1 to 3, e has a value ranging from 0 to 2, and d+e has avalue ranging from 1 to 3, all other units optionally being units of theformula: ##EQU4## in which W is as defined above, and g has a valueranging from 0 to 3. All the limiting values of a, b, c, d, e and g areinclusive.

The compound (1) can be formed exclusively of units of formula (1) orcan contain, in addition, units of formula (2).

Compound (1) can have a linear, branched, cyclic or network structure.The degree of polymerization thereof is 2 or more, and is generally lessthan 5000.

Y is generally a vinyl radical and Z is generally selected from methyl,ethyl and phenyl radicals.

The compounds (1) are well known to this art and are described, forexample, in U.S. Pat. Nos. 3,220,972, 3,344,111 and 3,434,366.

In the formulae (1) and (2) above, a can be an integer ranging from 1 to3, preferably 1; b is an integer ranging from 0 to 2, the sum of a+b hasa value ranging from 1 to 3 and c is an integer having a value rangingfrom 0 to 3.

Examples of silyloxy units of the formula (1) are thevinyldimethylsiloxane unit, the vinylphenylmethylsiloxane unit and thevinylsiloxane unit.

Examples of silyloxy units of the formula (2) are SiO_(4/2),dimethylsiloxane, methylphenylsiloxane, diphenylsiloxane, methylsiloxaneand phenylsiloxane units.

Examples of compounds (1) are polydimethylsiloxanes havingdimethylvinylsilyloxy end groups, polymethylvinylpolydimethylsiloxanecopolymers having trimethylsilyloxy end groups,polymethylvinylpolydimethylsiloxane copolymers havingdimethylvinylsilyloxy end groups and cyclic polymethylvinylsiloxanes.

The compound (2) according to the invention can be exclusively composedof units of the formula (3) or contains, in addition, units of theformula (4).

The compound (2) can have a linear, branched, cyclic or crosslinkedstructure. The degree of polymerization thereof is 2 or more, butgenerally less than 5000.

Group W has the same meaning as the group Z above.

In the formulae (3) and (4) above, d is an integer ranging from 1 to 3,preferably 1; e is an integer ranging from 0 to 2, the sum of d+e rangesfrom 1 to 3 and g is an integer ranging from 0 to 3.

Examples of units of the formula (3) are:

H(CH₃)₂ SiO_(1/2), HCH₃ SiO_(2/2), H(C₆ H₅)SiO_(2/2).

The examples of units of the formula (4) are the same as those givenabove for the units of the formula (2).

Examples of compound (2) are:

polydimethylsiloxanes having hydrodimethylsilyloxy end groups,polydimethylpolyhydromethylsiloxane copolymers having trimethylsilyloxyend groups, polydimethylpolyhydromethylsiloxane copolymers havinghydrodimethylsilyloxy end groups, polyhydromethylsiloxanes havingtrimethylsilyloxy end groups and cyclic polyhydromethylsiloxanes.

The ratio of the number of hydrogen atoms linked to the silicon in thecompound (2) to the number of alkylenically unsaturated groups in thecompound (1) ranges from 0.4 to 5, and preferably from 0.6 to 2. Thisratio can, however, range from 2 to 5 if it is desired to make elastomerfoams.

The compound (1) and/or the compound (2) can be diluted in an organicsolvent which is compatible with the silicones.

The compositions can contain, in addition to the usual additives,depending upon their fields of intended use, such as reinforcing and/ornon-reinforcing fillers for elastomeric compositions (pyrogenic silica,precipitated silica, ground quartz, calcium carbonate, and the like),inhibitors for elastomeric compositions and thin layer coatingcompositions, such as the acetylene derivatives described in U.S. Pat.Nos. 3,445,120 and 4,347,346, polydimethylsiloxane oils blocked at theirpolymer ends with trimethylsilyloxy groups, and the like.

The compositions of the invention can be used as such (neat) or dilutedin an organic solvent.

The crosslinking of these compositions is performed at a temperatureranging from room temperature to 200° C., depending upon the type ofcomposition and the amount of catalyst.

The curing temperature generally ranges from 60° to 140° C. The amountof catalyst by weight, calculated as weight of platinum metal, generallyranges from 2 to 600 ppm, typically from 5 to 200 ppm, based on thetotal weight of the composition.

The complexes according to the invention are compounds which are fairlyeasy to prepare, are stable on storage over very long periods at roomtemperature and retain their reactivity for a very long period. They arevery reactive in small amounts and are especially useful in coldvulcanizable (RTV) elastomer compositions and in coating compositions,either with or without solvents, for imparting non-stick properties.

For this latter application, the compositions of the invention can hencebe used either as such or diluted in a solvent. When they are dispersedor diluted in a solvent, a volatile organic solvent which is compatiblewith the composition is used, selected, for example, from alkanes,petroleum cuts containing paraffin compounds, toluene, heptane, xylene,isopropanol, methyl isobutyl ketone, tetrahydrofuran, chlorobenzene,chloroform and 1,1,1-trichloroethane. The solvent preferably constitutesfrom 50 to 99% by weight of the dis- persion.

By evaporation of the solvent from the dispersion, the compositionhardens, and these dispersions are thus useful as coating compositionsfor metal, wooden or glass articles and for flexible sheets of paper,plastic, and the like.

The solvent-free compositions can also be used to make a material, suchas metal foils, glass, plastics or paper, non-adherent to othermaterials to which it would normally stick. In the case of asolvent-free composition, the composition advantageously has a viscositynot exceeding 5000 mPa.s, and preferably ranges from 10 to 4000 mPa.s at25° C., and the ratio of the hydrogen atoms bonded to the silicon in (2)to the sum of the alkenyl radicals bonded to the silicon in (1) is atleast 0.5 : 1, and generally less than 2 : 1, this ratio also beingapplicable to the resins with solvent. Furthermore, the compounds (1)and (2) are polymers and/or copolymers having substantially linearchains.

The solvent-free, that is to say, undiluted, compositions are applied bymeans of devices which are suitable for depositing small amounts ofliquids in a uniform manner. For this purpose, there may be used theso-called "transfer coating" device which incorporates, in particular,two superposed rollers; the function of the lower roller, which dipsinto the coating bath in which the compositions are present, is toimpregnate the upper roller with a very thin layer, and the function ofthe latter roller is then to deposit onto the paper the desired amountsof the compositions with which it is impregnated, such control ofquantities being achieved by adjustment of the respective speeds of thetwo rollers which rotate in opposite directions. The dilutedcompositions, that is to say, those with a solvent, can be applied bymeans of devices used on industrial machines for coating paper, such asthe engraved "thousand dot" roller and machines for the so-called"reverse roll" system.

Once deposited onto the supports, the compositions are hardened in a fewseconds by passing same through tunnel ovens heated to 60°-200° C., thepassage time through these furnaces varying generally from 2 to 30seconds. This time depends, for a given oven length, on the speed atwhich the coated supports travel (this speed can exceed 200 meters perminute); in general, a support consisting of cellulosic material travelsfaster (for example, at a speed of 3 m/second for a temperature greaterthan 140° C.) than a plastic-based support. In effect, this lattermaterial cannot withstand the effect of high temperatures, and it willtherefore be subjected to a lower temperature but for a longer period,for example, it will travel at a speed of 0.75 m/second for atemperature on the order of 80° C.

The amounts of compositions deposited onto the supports can vary, andmost frequently range from 0.1 to 5 g/m² of treated surface. Theseamounts depend upon the nature of the supports and the non-stickproperties sought. Such amounts most frequently range from 0.5 to 1.5g/m² for non-porous supports.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are given, it being understoodthat same are intended only as illustrative and in nowise limitative. Insaid examples to follow, all percentages and parts are given by weight,unless otherwise indicated.

EXAMPLE 1

Preparation of a platinum/β-myrcene complex:

A platinum/triene complex was prepared by mixing:

(i) 1 part of H₂ PtCl₆.6H₂ O;

(ii) 5 parts of isopropanol;

(iii) 2 parts of sodium bicarbonate NaHCO₃ ; and

(iv) 6 parts of β-myrcene.

The chloroplatinic acid was first dissolved in the isopropanol, NaHCO₃was then added in small portions to avoid the formation of foam, sincecarbon dioxide was evolved, and the β-myrcene was then added.

The mixture was treated under reflux for 20 min at approximately 80° C.under stirring. The original orange coloration changed to yellow. Thereaction mixture was cooled to room temperature and the isopropanolremoved at 20° C. under a vacuum of 15 mbar. The inorganic impuritieswere precipitated in hexane and, after filtration, the solution wasconcentrated at 40° C. under a vacuum of 1.0 to 10 mbar. An orange-redoil was obtained in 80% yield relative to the total weight of platinumand of initial reagents. A Cl/Pt ratio of 1.0 was obtained. Theconcentration of the complex was reduced to 3% by dilution in toluene.This solution was used in the subsequent steps.

EXAMPLE 2

The procedure of Example 1 was repeated, except that the treatment underreflux was for 15 min. A Cl/Pt ratio of 1.4 was obtained.

EXAMPLE 3

The procedure of Example 1 was repeated, except that the treatment underreflux was for 8 min. A Cl/Pt ratio of 1.9 was obtained.

EXAMPLE 4

The procedure of Example 1 was repeated, except that the treatment underreflux was for 30 min. A Cl/Pt ratio of 0.9 was obtained.

EXAMPLE 5

The procedure of Example 1 was repeated exactly, except that theβ-myrcene was replaced by β-springene. A Cl/Pt ratio of 1.0 wasobtained.

COMPARATIVE EXAMPLE 6C

Synthesis of a platinum/styrene complex:

The procedure of Example (1) of European Pat. No. 57,459 was repeatedexactly, except that the refluxing temperature and reaction time wasrespectively 75°-77° C. and 30 min. The complex was obtained withdifficulty in the form of a black tar having a Cl/Pt ratio of 2.5, andthis was subsequently used in 3% solution in toluene.

EXAMPLE 7

Reactivity of the platinum/β-myrcene and /β-springene complexes insolvent-free compositions for rendering paper non-sticking:

A treatment bath was prepared according to the following procedure:

100 parts of a silicone composition were formulated, containing:

(a) 90.5% of a polydimethylsiloxane copolymer having vinyl units in thechain and with a dimethylvinylsilyloxy end group, having approximately3% by weight of vinyl groups and having a viscosity of approximately 250mPa.s at 25° C.;

(b) 2.5% of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane;and

(c) 7% of a polymethylhydrosiloxane fluid having a trimethylsilyloxy endgroup, used as a crosslinking agent and comprising approximately 1.5% byweight of hydrogen atoms bonded to silicon, and having a viscosity ofapproximately 20 mPa.s at 25° C.

To this bath there were added:

(d) 60 ppm of platinum (3×10⁻⁴ g-at. of Pt/kg of composition) in theform of a platinum complex prepared in Examples 1, 2, 3 and 5.

The mixture was stirred vigorously at room temperature for a fewminutes, and this mixture was then, without using a solvent, depositedonto paper (approximately 1 g of mixture per m²) by means of a coatingrod, and the silicone composition was hardened in a forced-aircirculation oven set to a variable temperature.

The hardening time of the silicone coating was thus studied by notingthe minimum residence time in the oven needed to obtain a fully-hardenedcoating. The results obtained are reported in Table I below:

                  TABLE I                                                         ______________________________________                                                       Crosslinking time                                                             (in seconds)                                                   Nature of the  (Oven temperature)                                             catalyst       (110° C.)                                                                            Cl/Pt                                            ______________________________________                                        Example 1      15            1.0                                              Example 2      17            1.4                                              Example 3      20            1.9                                              Example 5      25            1.0                                              (*)            30            4.6                                              H.sub.2 PtCl.sub.6.6H.sub.2 O                                                                >120          5.9                                              Example 6C     >60           2.5                                              ______________________________________                                         NB: (*) catalyst which is the product of reaction of chloroplatinic acid      with octanol, according to U.S. Pat. No. 3,220,972.                      

EXAMPLE 8

To 100 g of polydimethylsiloxane oil having dimethylvinylsilyloxy endgroups (0.4% by weight of vinyl groups relative to the weight of thepolymer) having a viscosity 600 mPa.s at 25° C. there were added 45.0 gof pyrogenic silica having a specific surface of 300 m^(2/) g andtreated with hexamethyldisilazane. To this mash was added anorganosilicone composition containing:

(a) 1.7 g of a polydimethylsiloxane copolymer having hydromethylsilyloxyunits in the chain, possessing, relative to the weight of the polymer,0.24% of hydrogen atoms bonded to silicon and having approximately 120atoms of silicon per molecule;

(b) 8 g of a polydimethylsiloxane polymer having dimethylhydrosilyloxyend groups and a viscosity of 30 mPa.s at 25° C.; and

(c) x ppm of platinum metal in the form of a platinum/β-myrcene complexcatalyst in 3% strength solution, prepared as in Example 1. After beingmixed, the composition crosslinked at room temperature, and the increasein viscosity of the composition with time and the top/bottom Shore Ahardness of the test pieces formed after 24 hours of crosslinking weremeasured. The results are reported in Table II below:

                  TABLE II                                                        ______________________________________                                        Nature of the                                                                 catalyst and                                                                  content of Pt                                                                              Stability of the                                                                          Shore A hardness                                     metal in ppm bath        (top/bottom) (**)                                    ______________________________________                                        (*)          3 h         20/23                                                8 ppm                                                                         Example 1    3 h         19/23                                                8 ppm                                                                         Example 1    2 h         20/22                                                12 ppm                                                                        ______________________________________                                         NB: (*) Catalyst which is the product of reaction of chloroplatinic acid      with octanol, according to U.S. Pat. No. 3,220,972.                           (**) Top = hardness measured on the face surface of the test piece expose     to the air                                                                    Bottom = hardness measured on the face surface of the test piece in           contact with the base of the mold.                                       

While this invention has been described in terms of various preferredembodiment, the skilled artisan will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims, including equivalents thereof.

What is claimed is:
 1. A platinum/olefin complex comprising halogenvalues, the olefin moiety thereof which comprises an aliphatic trienehaving the general formula: ##STR7## wherein R₁ is a linear or branchedchain alkyl radical having from 1 to 6 carbon atoms, and R₂ is R₁ or alinear or branched chain alkenyl radical having from 2 to 16 carbonatoms and at least one site of ethylenic unsaturation, and said complexhaving a ratio, in gram-atoms of halogen to gram-atoms of platinum,ranging from virtually 0 to
 4. 2. The platinum/olefin complex as definedby claim 1, said olefin moiety comprising β-myrcene.
 3. Theplatinum/olefin complex as defined by claim 1, said olefin moietycomprising β-farnesene.
 4. The platinum/olefin complex as defined byclaim 1, said olefin moiety comprising β-springene.
 5. Theplatinum/olefin complex as defined by claim 1, said ratio ranging fromvirtually 0 to
 2. 6. The platinum/olefin complex as defined by claim 1,wherein R₁ is methyl.